The U.S. Department of Homeland Security (DHS) is quietly building what will likely become the largest database of biometric and biographic data on citizens and foreigners in the United States. The agency’s new Homeland Advanced Recognition Technology (HART)database will include multiple forms of biometrics—from face recognition to DNA, data from questionable sources, and highly personal data on innocent people. It will be shared with federal agencies outside of DHS as well as state and local law enforcement and foreign governments. And yet, we still know very little about it.